Polyurethane based materials have been employed for use in the biomedical field for device implants as they exhibit good biocompatibility. Examples of such applications include indwelling catheters, intra-aortic balloons and mammary implants. Most biomedical polyurethane applications emphasize and focus on material physical properties, such as bio-stability, modulus, hardness, and elongation, however, many other biomedical applications, such as tissue engineering, require polyurethanes that rapidly degrade and form nontoxic by-products.
One of the unique aspects and advantages of polyurethanes is that their mechanical properties may be precisely tuned by changes in the ratio of monomers used in a polyurethane polymerization. For example, segmented polyurethanes produced from different types of monomers (soft blocks and hard blocks) phase segregate into soft rubbery segments and hard glassy segments, depending on the monomers selected. Therefore, if an application requires a soft flexible material with a high percentage of a monomer contributing to a soft segment, those skilled in the art may adjust the monomer ratios accordingly.
In the case of tissue engineering, elastomeric materials, such as polyurethanes, may be used to provide flexible scaffolds for cell growth. In some cases, hydrolyzable soft polymer segments such as polylactide (PLA) and polycaprolactone (PCL) have been incorporated into polyurethanes to make them degradable by ester linkage hydrolysis in vivo. One of the difficulties with the current approach is the adjustment of the rate of degradation, which can often times take months, and create toxic by-products which produce undesirable effects that counter or inhibit tissue scaffolding. Therefore, there is a need for new biodegradable and biocompatible polyurethanes that degrade more quickly than existing materials and produce non-toxic byproducts.